Bushing sealing cap



April 27, 1937. G. A. BURR ET AL BUSHING SEALNG CAP Filed March 29, 1954 INVENTORS. Gordon //.Bu' E Edwin E Hl 0/ Patented Apr. 27, -1937 UNITED STATES BUSHI'NG SEALING @AP Gordon A. Burr, Wilkinsburg',

and Edwin E.

Arnold, Pittsburgh, Pa., assignors to Wasting house Electric & Manufacturing Company, East Pittsburgh, Pa., a corporation oi' Pennsylvania Application March 29, i934, Serial No. 'illiil Our invention relates to insulating bushings commonly used to protect the leads of encased high-tension electrical apparatus, such as transformers and circuitv breakers, and, more particularly, to an improved bushing construction whereby relative movement of the bushing parts under the influence of temperature variations is permitted Without injury to the bushing ele ments, and without affecting the insulating char-u acteristics of the bushing 'as a Whole.

Bushings of the type now generally used comprise a substantially cylindrical Weather casing adapted to be mounted on the tank of a transformer, for example, and a conductor extends axially of the casing into the taule for connection with'the transformer Winding. The free end of the conductor extends beyond the upper end of the casing for connection with the circuit tutti which the transformer is to be associated. The conductor and casing are secured together at both ends of the casing to form a fluid-tight chamber for an insulating fluid which surrounds the conductor and substantially iills the casing.

Such bushings are generally exposed to varying Weather conditions With temperature ranging from below zero to over lilo" l., and in view of the dissimilarity in coemcients of thermal expansion of the conductor and casing, as well as volumetric changes in the insulating fluid, considerable difficulty has been experienced in maintaining a, duid-tight joint between the ends of the casing and the conductor.

It is an object oi our invention, therefore, to provide a bushing construction which shall be fluid-tight over a Wide range of temperature values.

It is a further object of our invention to provide, in a bushing construction ci the luid=iilled type, a seal betueen the conductor and the open end of the weather-casing which will permit relative axial expansion of these elements and, at the same time, serve as a'. reservoir for insulating fluid.

In practicing our invention, We provide a seal comprising an expansible chamber surrounding the conductor and resting" upon the upper end vof the Weather casing, and means cooperating with the conductor engaging the upper exterior face of the chamber for compressing the latter to maintain it in operative position.

Referring more specifically to the drawing,v

Figure l is a view in elevation oi acornplete bushing unit constructed in accordance with present invention.

Fig. 2 is a view in vertical section oi a portion of the structure shown ln Fig. l.

Referring to Fig. l", the bushing assembly coin= prises an elongated conductor 2 which may, as

' in the present embodiment, be wrapped with a 60 plurality of alternate'layers of conducting and insulating material to constitute a bushing of the condenser type. 'llfie upper haii of the cona ductor is enclosed in a weather-casing of porcelain or other suitable dielectric material and is provided with creepage :danges t in accordance with usual practice.

A metallic mounting @ange surrounds the Wrapped conductor in duid-tight relation and constitutes a support for the Weather casing, a suitable gadget l being interposed between abutting faces oi the casing and flange to provid a duid-tight joint.

in practice, the lower haii oi the conductor is inserted tluough an -@penning in the tant: of a transformer or circuitbreakeri and the bushing assembly is maintained in position by suitable ineans securing tire ieterally extending flange G to the around the opening therein. l'uis type of construction is common practice and need not be described in detail.

The bushing is adapted to be Jilled with an insulating fluid which may be more or less viscous, suoli as-aspiieituni or oil.

Referring more particularly to Fig. 2, the con ductor 2 above the upper edge of the casing d and the two aie secured in operative relation by oisans of a cbambered casting i@ which is substantiallyr ot bowl-shape and is provided with a central aperture to permit the end of the conductor extend therethrough.

Trie external contour oi the casting is rounded to reduce the concentration oirthe electrostatic liield at this end ci tire bushing, which is to be connected to the high-tension line, to obtain an improved stress distribution between the top oi the casing and the grounded flange line casting iii, in tbe present embodiment, is an aluminum alloy which is sumciently dense to prevent the leakage of the insulating fluid through its walls, and its side walls are relatively thin: to permit a limited expansion and contraction oi the casting serially oi the conductor.

Within the casting it), and depending from the top thereof, legs il are provided .winch cooperate with a i2 on the bottom or the casting. in practice the legs and seat may be integrai and subsequently separated by a machining operation. Although this particular procedure is not essentiai, it is an efficient Way to obtain an accurate spacing between the ends of the legs ii and seat i2.

The lower face oi the casting is provided with peripheral seat adapted to rest upon the upper edge of the weather casing (l, and a gasket iii is in'frposed between the engaging faces to provide e, cushioned -duid-tiglut joint. The inner peripheral edge of the bottom wall of the casting is provided with a depending tlange it which eatends into tbe casing (l, as sneu/n. A

The upper tv'all of the casting is provided with f installation or subsequent removal.

an interiorly-threaded axially extended flange I5 and means defining a recess surrounding the conductor 2. Packing, such as asbestos rope I6 impregnated with a suitable viscous compound which will not harden with age, is disposed in said recess, and is compressed in position to provide a fluid-tight seal by means of a packingnut I1 which cooperates with the interior threads of the flange I5. After the packing nut has been seated it is sealed in position by a quantity of sealing material I8 of the molded type, such as Bakelite The casting l is maintained in position by means of a cap 20 which is provided with a threaded opening for cooperation with the threaded end of the conductor 2, and has a depending flange 2| adapted to surround the flange I on the casting to provide a weather-shed. The lower face of the cap 20 is adapted to engage the upper edge of the flange I5 and, if desired, a gasket 22 may be inserted therebetween to provide a resilient fluid-tight seal therebetween. Ears 23 on the cap 2li may be provided to facilitate handling of the bushing during its The upper end of the threaded opening in the cap may be chamfered, as shown, to receive a ring of solder 24.

In assembling the structure described, the casing 4 is filled with an insulating fluid 25 and some of the iiuid is disposed in the casting I0 before it is placed in position on the casing 4 with the gasket I3 between the engaging surfaces. The volume of insulating fluid is so chosen that its minimum height, under various temperature conditions, will be level with or slightly above the upper edge of the casing 4, so that the fluid is maintained in contact with the gasket I3 to further insure that air and moisture may not be drawn intov the casing at this point.

The packing I6 is then placed in position and compressed by means of the packing-nut I1 to obtain a fluid-tight joint between the top of the casting and the conductor 2.

The casting is then compressed within its elastic limit, so that the legs Il abut the seat I2 and cap 20 is screwed down upon the gasket 22 and flange I5 to maintain the casting in its compressed condition, and to compress the gasket I3 to maintain a positive uid-tight joint betweenl the bottom of the casting III and the casing 4. 'I'he amount thel casting I0 may be compressed is limited by the three legs II, but is suiilcient to insure that subsequent expansion oi' the casting may occur under the varying temperature conditions encountered in practice, without disrupting the seal at the gasket I3.

It should be apparent from the foregoing that under conditions of relative movement between the conductor 2 and casing 4, the expansible casting I0 will follow such movements and maintain a fluid-tight seal between the conductor and casing. Although it is true that such relative movement will be small, it has been found, in prior constructions, to be suiilcient to break the seal between the conductor and casing, permitting the insulating fluid to escape or permitting air and moisture to bedrawn into the casing. These diiiiculties have been eliminated in the construction of our invention.

In order to permit testing of the Huid-tight character of the bushing, after assembly, a plug 26 may be provided in the upper face of the casting so that the interior of the bushing may be subjected to a fluid pressure or vacuum. as desired.

Various modifications may be made in our invention without departing from the spirit and scope thereof, and we desire that the invention shall be limited only by the scope of the appended claims.

We claim as our invention:

l. In ai bushing for high-tension electrical apparatus including an elongated cylindrical casing of insulating material, a conductor extending therethrough with its free end projecting beyond the end of said casing, and a quantity of insulating fluid substantially filling said casing, means' constituting a combined fluid reservoir and expansion chamber for securing the free end of said conductor to the end of said casing in fluidtight relation and premitting relative axial expansion of said conductor and casing, comprising a chambered casting having a rounded exterior surface and being expansible axially of the conductor, one face of said chamber being proportioned to engage the upper edge of said casing, means cooperating with said conductor engaging the other face of said chamber for compressing and deforming said chamber to maintain itin operative position, and means for limiting the compressive movement of said chamber.

2. In a bushing for high-tension electrical apparatus comprising a cylindrical casing of insulating material having a conducting rod extending axially therethrough, one end of said casing being rigidly mountedwith respect to said conductor and the free end of said casing terminating adjacent to the free end of said conductor, an axially expansible member of bowlshape having an axial aperture to permit the conductor to extend therethrough and having a lower face proportioned to rest upon the end face o1' said casing, means on the upper part of said member for embracing said conductor in fluidtight relation, and means engaging said conductor for compressing said member a sufficient amount to maintain it in operative position throughout the range of relative axial expansion and contraction of the conductor and casing.

3. In a bushing comprising a cylindrical casing of insulating material having a conducting rod extending axially therethrough. one end of said casing being rigidly mounted with respect to said conductor and the free ,end of said casing terminating adjacent to the free end of said conductor, an axially expansible member of bowlshape having an axial aperture to permit the conductor to extend therethrough and having a lower race proportioned to rest upon the end face of said casing, means on the upper part of said member for embracing said conductor in fluidtight relation, means cooperating with said conductor for exerting a compressive force on said member to maintain it in operative position, a quantity of insulating fluid filling said casing and partially filling said expansible member, and means within said member for limiting the compressive movement thereof.

GORDON A. BURR. EDWIN E. ARNOLD. 

